Sepsis syndrome is the 11th leading cause of death in the United States accounting for ~ 210,000 deaths annually. Although the pathophysiology of sepsis syndrome is complex, new therapies, in addition to antimicrobials, are urgently needed. Adenosine is a pluripotent molecule released in times of stress such as trauma, ischemia, and infection. Molecular cloning, pharmacological and functional analysis has identified four G protein coupled adenosine receptor (AR) subtypes, A1p A2A, A2B and A3. Activation of A2AARs produces an anti anti-inflammatory effect in multiple cell types including neutrophils, monocytes, macrophages, and, potentially, T cells. We have found that A2A adenosine receptor (A2AAR) agonists are strongly protective in mouse models of endotoxemia and following live bacterial challenge resulting in septic shock. This proposal is designed to study some of the mechanisms responsibe for this protective effect, and identify particular cellular targets in vivo mediating protection by A2AAR agonists. In aim 1 we will determine serum cytokine/chemokine profiles following challenge with LPS or live bacteria with or without the administration of an A2AAR agonist. We will focus on several potential mediators and/or receptors implicated in the pathophysiology of septic shock, including TNF?, IL-1, IL-6, IL-8, IL-10, IL-12, interferon-?, MIF, HMGB1, and TREM-1. In specific aim 2 we will use chimeric mice to explore the potential interaction of A2AAR agonist with cellular targets from hematopoeitic cell lineage and/or other cells (e.g. endothelial cells). We have generated mice lacking the A2AAR (A2A knockouts; A2AKO) and will examine bone marrow transplantation between A2AKO and wild type mice to approach this problem. In aim 3 we will further refine our conclusions by utilizing the Cre-loxp system of mouse genetics. This approach permits targeted deletion of the A2AAR in specific cell types such as T cells, myeloid cells, including granulocytes and/or endothelial cells. These complimentary approaches will permit a full understanding of the cellular targets responsible for A2AAR activation as a protective mechanism in sepsis/septic shock, are crucial to furthering our understanding of A2AAR activation and its protective effects in septic states but also would provide a rationale for investigation in the use of this class of compounds for treating additional inflammatory diseases in humans.